Mauro Lomer

A quasi-distributed level sensor based on a bent side-polished plastic optical fibre cable

A flexible quasi-distributed liquid level sensor based on the changes in the light transmittance in a plastic optical fibre (POF) cable is proposed. The measurement points are constituted by small areas created by side-polishing on a curved fibre and the removal of a portion of the core. These points are distributed on each full turn of a coil of fibre built on a cylindrical tube vertically positioned in a tank. The changes between the refractive indices of air and liquid generate a signal power proportional to the position and level of the liquid. The sensor system has been successfully demonstrated in the laboratory, and experimental results of two prototypes with 15 and 18 measurement points in a range of 33 mm and 39 mm respectively and a resolution of 0.08 mm with bend radii of 5 mm and 8 mm are presented.

An accurate photonic capacitance model for GaAs MESFETs

A new set of pseudoempirical equations is presented in order to simulate the optical and bias dependencies of GaAs MESFET junction capacitances, which is valid for the whole I-V plane. The variations induced in the small-signal equivalent circuit by the optical illumination are extracted from on-wafer scattering parameter measurements. New linear and quasi-logarithmic variations versus the incident optical power are shown for gate-drain and gate-source (Cgd and Cgs) capacitances. Furthermore, experimental results are in very good agreement with the simulated values for a wide range of optical power and bias conditions. Large signal MESFET models show a better fit with measured S-parameters than those previously published, leading to a greater degree of confidence in the design of photonic monolithic microwave integrated circuits.

Fiber Specklegram-Multiplexed Sensor

In this study, several multiplexing techniques have been combined to achieve a fiber specklegram multiplexed sensor. Using a single CCD camera as detector, two lasers of different wavelengths have been launched into two multimode polymer optical fibers and then combined through a 2 x 2 coupler before their interrogation. Both coupler exit fibers have been projected to different CCD positions and by analyzing each color of the video sequence, the four fiber channels can be independently obtained. In addition, the speckle sensitivity has been also studied analyzing different properties of speckle patterns such as their contrast or the speckle size. The achieved results will be very useful to the development of new fiber specklegram sensors with several sensing areas using only a CCD camera as detector, making possible low cost sensing devices.

Low cost plastic optical fiber sensor based on surface plasmon resonance

Surface plasmon excitation using a variation of Kretschmann method based on light guiding through an optical fiber has been extensively studied in the literature. But, due to its particularly bad propagation conditions, plastic optical fiber was not taken into account in documented experiments. We propose a low cost sensor using this type of fiber, in which we try to avoid the problems both through careful design and signal processing. First of all we discuss the sample fabrication and measurement in section 2; then the results obtained are discussed in section 3, including the problems faced because of the multimode character of the fiber, for which we propose alternative sample shapes as a mean of reducing them. As a conclusion we propose a roadmap to design a low cost sensor based in the structures studied in this paper.

Speckle characterization in multimode fibers for sensing applications

This paper proposes the characterization of speckle patterns of multimode fibers in view of sensing applications and particularly for detection of vibration or seismic activity. Plastic optical fibers are used in this work due to its excellent flexibility and adaptability to build sensor heads. We are interested in the response to vibration, for which we use a short cylindrical piezoelectric transducer (PZT) vibrating in radial direction. The multimode fiber was coiled as tightly as possible around the mandrel of the PZT and periodic stretching effect was caused by the radial oscillations of the actuator. The PZT is modulated with a frequency generator by applying a sinusoidal signal in the range of 0 to 20 Hz, so the speckle patterns can be time averaged. The fiber extreme is attached to a high speed camera with a plastic adaptor, centering the speckle pattern into the CCD. Maintaining the fiber position, a region of interest is selected to capture the video sequence and it is captured to detect the variations in the speckle pattern. Once having the video sequence, it is processed by averaging the pixel differences between two consecutive frames. This processed sequence is also filtered in order to reduce the high frequency noise component. In this work we report the results of the characterization of 3 types of multimode fibers, with core diameters of 50 μm, 240 μm and 980 μm.

Principle of functioning of a self-compensated fibre-optical displacement sensor based on diffraction-grating-ended POF

A self-compensated displacement sensor has been realized by placing a diffraction grating on the end face of a plastic optical fibre (POF), the method serving for any highly multimode optical fibre. By measuring the output powers at two diffraction angles corresponding to two different diffraction orders, a simple way to cancel out the fluctuations of the light source and other disturbances has been achieved.

New low-cost fiber optic accelerometer system for stator winding monitoring of hydroelectric generating machines

A new fiber optic accelerometer system for stator winding simultaneous multi-point vibration monitoring of hydroelectric generating sets is presented. It is composed of as many sensor heads as points to be monitored, an optical channel and a processing unit distant from the sensing area, which is exposed to strong electromagnetic interference. The evaluation scheme is based on an intensity modulation and differential detection technique so that the measure is not influenced by external perturbations. The system is able to measure accelerations ranging from 30 to 450 Hz, with a maximum amplitude of 200 m/s2 RMS. Experimental results for the previous prototypes developed are showed. This sensor is intended to be integrated in a new complex system aimed to reach the goals of instantaneous protection, real time detection and evaluation of defects, failures and malfunctions in the above mentioned machines.

POF vibration sensor based on speckle pattern changes

A method of sensing vibration using detection of changes in the spatial distribution of energy on the speckle pattern in the output multimode optical fiber is presented and demonstrated. The implementation of sensor consists of a small length of fiber which is isolated and sensitive to ambient vibration. The projection of the speckle pattern is directly recorded by a CCD camera at the outlet end of the fiber and processed changes in the intensity distribution. The sensor is simple, inexpensive and can be implemented to measure vibrations in engine, machines or buildings.

Measurement of displacement in the micrometer range using speckle pattern correlation in multimode fibers

The displacement measurement in the micrometer range using the speckle pattern correlation in optical fibers is described. The high sensitivity of a multimode fiber when propagating a coherent light causes any variation in the distribution of the speckle pattern is proportional to the disturbance which it originates. The speckle pattern is caused by interference between modes and the shift mechanism is due to coupling between modes and micro-induced redistribution curvature applied to the fiber externally. The movement is produced by a transducer containing microbends pressure induced on the fiber. Experimental results are presented using three types of multimode plastic optical fiber. In the signal generated from the change in the speckle pattern observed with relatively good reproducibility, so that sensor systems could be used.

Comparison between a symmetric bidirectional-pumping and a unidrectional-pumping configurations in an erbium fiber ring laser

An experimental comparative study between two wide-band wavelength-tunable erbium doped fiber ring lasers (EDFRLs) with the same active fiber length but with two different pumping configuration (forward unidirectional pumping and symmetric bidirectional pumping) is reported in this paper. Both fiber lasers cover almost the whole C-band and L-band with a single setup laser. The signal wavelength can be tuned in a wide range of 60 nm with the two presented lasers. Nevertheless, experimental results verify that a higher output power is obtained with the bidirectional pump configuration.